/**
 * Base64 encode / decode 利用系统原生的实现

	_$.base64encode = window.btoa ? function ( str ) {
	    return window.btoa(unescape(encodeURIComponent( str )));
	} : Base64.encode;
 
	_$.base64decode = window.atob ? function ( str ) {
	    return decodeURIComponent(escape(window.atob( str )));
	} : Base64.decode;

 * http://www.cnblogs.com/rubylouvre/archive/2010/09/19/1829898.html
   http://www.planabc.net/2010/07/21/base64_encoding_in_javascript_part_i/
   https://bitbucket.org/davidchambers/base64.js/src/d29f8a098a55?at=default
   https://developer.mozilla.org/en-US/docs/DOM/window.btoa
 * http://www.webtoolkit.info/
 */
define(function(require, exports, module) {
	var Base64 = {
		// private property
		_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
		
		// public method for encoding
		encode : function (input) {
		    var output = "";
		    var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
		    var i = 0;
		
		    input = Base64._utf8_encode(input);
		
		    while (i < input.length) {
		
		        chr1 = input.charCodeAt(i++);
		        chr2 = input.charCodeAt(i++);
		        chr3 = input.charCodeAt(i++);
		
		        enc1 = chr1 >> 2;
		        enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
		        enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
		        enc4 = chr3 & 63;
		
		        if (isNaN(chr2)) {
		            enc3 = enc4 = 64;
		        } else if (isNaN(chr3)) {
		            enc4 = 64;
		        }
		
		        output = output +
		        this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
		        this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);
		
		    }
		
		    return output;
		},
		
		// public method for decoding
		decode : function (input) {
		    var output = "";
		    var chr1, chr2, chr3;
		    var enc1, enc2, enc3, enc4;
		    var i = 0;
		
		    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
		
		    while (i < input.length) {
		
		        enc1 = this._keyStr.indexOf(input.charAt(i++));
		        enc2 = this._keyStr.indexOf(input.charAt(i++));
		        enc3 = this._keyStr.indexOf(input.charAt(i++));
		        enc4 = this._keyStr.indexOf(input.charAt(i++));
		
		        chr1 = (enc1 << 2) | (enc2 >> 4);
		        chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
		        chr3 = ((enc3 & 3) << 6) | enc4;
		
		        output = output + String.fromCharCode(chr1);
		
		        if (enc3 != 64) {
		            output = output + String.fromCharCode(chr2);
		        }
		        if (enc4 != 64) {
		            output = output + String.fromCharCode(chr3);
		        }
		
		    }
		
		    output = Base64._utf8_decode(output);
		
		    return output;
		
		},
		
		// private method for UTF-8 encoding
		_utf8_encode : function (string) {
		    string = string.replace(/\r\n/g,"\n");
		    var utftext = "";
		
		    for (var n = 0; n < string.length; n++) {
		
		        var c = string.charCodeAt(n);
		
		        if (c < 128) {
		            utftext += String.fromCharCode(c);
		        }
		        else if((c > 127) && (c < 2048)) {
		            utftext += String.fromCharCode((c >> 6) | 192);
		            utftext += String.fromCharCode((c & 63) | 128);
		        }
		        else {
		            utftext += String.fromCharCode((c >> 12) | 224);
		            utftext += String.fromCharCode(((c >> 6) & 63) | 128);
		            utftext += String.fromCharCode((c & 63) | 128);
		        }
		
		    }
		
		    return utftext;
		},
		
		// private method for UTF-8 decoding
		_utf8_decode : function (utftext) {
		    var string = "";
		    var i = 0;
		    var c = c1 = c2 = 0;
		
		    while ( i < utftext.length ) {
		
		        c = utftext.charCodeAt(i);
		
		        if (c < 128) {
		            string += String.fromCharCode(c);
		            i++;
		        }
		        else if((c > 191) && (c < 224)) {
		            c2 = utftext.charCodeAt(i+1);
		            string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
		            i += 2;
		        }
		        else {
		            c2 = utftext.charCodeAt(i+1);
		            c3 = utftext.charCodeAt(i+2);
		            string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
		            i += 3;
		        }
		
		    }
		
		    return string;
		}
	};

	module.exports = Base64;
});